1. Field of the Invention
This invention relates to a malfunction detecting system of an engine cooling apparatus, more particularly to a malfunction detecting system of a radiator, still more particularly to a malfunction detecting system of a radiator thermostat.
2. Description of the Related Art
The internal combustion engine of a vehicle is equipped with a radiator (cooling apparatus) for cooling a coolant. The radiator is connected midway of a coolant communicating passage composed of an inlet pipe and an outlet pipe. A thermostat (shut-off valve) is installed in the communicating passage. The thermostat closes the communicating passage when the coolant temperature is low, such as just after engine starting, and opens it as the coolant temperature rises so that the coolant can enter the radiator to be cooled.
Since the radiator is one of the on-board components of a vehicle, it is preferably checked for malfunction. It was for this purpose that the assignee developed a system that first checks whether the engine is in a state cooled to a temperature equal to the outside air temperature (intake air temperature) owing to thorough soaking (long-period or sufficient standing) and whether change in the outside air temperature since engine starting is small, and then, when these conditions are met, determines that the conditions for execution of malfunction detection have been established, whereafter it carries out a calculation for estimating the coolant temperature and determines that the radiator, more precisely the radiator thermostat, has malfunctioned if, for example, the detected coolant temperature has not reached the judge-normal value when the estimated coolant temperature reaches the judge-malfunction value. This technology is described in the assignee's Japanese Laid-Open Patent Application 2000-008853.